Replacement chair casters for modern office and task chairs. These feature the european pivot boss design, which makes the caster appear to be fully integrated to the formed nylon base of the chair. Be careful to measure the Pivot Boss Diameter, this unit features a 1-1/2" Pivot Boss and a 2-1/4" Mounting height. We also have available 1-3/4" Pivot Boss with a 2-1/8" mounting height. Capacity is 75 pounds per caster, so a chair with 5 can support more than 300 lbs. Designed to handle common abuse in an office or shop enivronment.